In the creation of an earth bore, the forward feed drive of such an earth boring machine moves the slide relatively slowly forwardly against a large force exerted by the earth, which force is transmitted to the slide through the boring rod. Previous earth boring machines have for the forward feed drive a cylinder arranged on the frame from which a piston is moved outwardly in its axial direction to push the slide forwardly. A disadvantage is that in such a drive, during the extension and retraction of the piston respectively, greatly different forces are created. The maximum force can therefore be deployed only either for the creation of a bore or for the pulling of the boring rod from the bore.
If the piston becomes fully extended, the boring rod is disconnected from the slide and thereafter the piston is retracted with the slide also being retracted on the frame oppositely to the forward feed direction. Thereafter, an additional rod member is fastened with one end to the slide and with its other end to the boring rod, before the piston is again driven forwardly to extend the bore. The frame of such earth boring machines extends at least over the length of the cylinder with its piston extended, and therefore, at least over double the length of a rod member. Where only little room is available for placement of the frame, such an earth boring machine cannot be used.
The frames of such earth boring machines can be built with shorter length. The publication DE 196 45 222 A1 discloses an earth boring machine on the frame of which is arranged a forward feed drive, and chains and chain wheels for driving a slide, which slide is fastened to an upper run of one of the chains. Such a construction requires a forward feed drive of high power for driving the slide at a low rotational speed and a large rotary moment. Therefore, arranged on the frame is an especially high power motor with a speed reducing drive which is expensive and requires a large amount of room.
If the chains are driven by an hydraulic motor, there arises the disadvantage that the hydraulic motor when operating at low rotational speeds has a very poor efficiency. This means that, especially in the case of hard earths, which demand a slow forward feed, the maximum rotational moment of the hydraulic motor becomes indeed needed but, because of the slow rotational speed, it cannot be used.
Further, during the forward feed of the slide against the resistance of the earth, large forces come into effect between the chain and the slide. This requires the use of especially robust chains and chain wheels likewise requiring much space so they are also disadvantageous in regard to constructional size and/or the space requirement of such compact boring mechanisms.
It is the object of the invention to provide an earth boring machine of the above kind which with an especially small space requirement creates in a simple way a large force for moving the slide in and opposite to the forward feed direction.